A burn-in test is performed as one of screening techniques for removing an initial failure of semiconductor devices. In the burn-in test, accelerated stress that is higher in temperature and pressure than that of the operation condition of the semiconductor devices is applied, thereby accelerating the occurrence of failures so that defective products can be removed in a short time. For example, a number of semiconductor devices that have been packaged are arranged on a burn-in board, and a supply voltage and input signal to be accelerated stress are applied in a high temperature bath for a given time. Thereafter, the semiconductor devices are removed outside, and judgment tests are performed as to acceptability in terms of their quality. In the judgment tests, judgments are done with respect to an increase of leakage current due to flaw of a semiconductor device, a defective product due to flaw in the multilayer interconnection, failure in the contact, and so on. A burn-in test is performed also in the state of a semiconductor wafer.
When the burn-in test of a semiconductor wafer is performed, for example, the test is done through an electrode pad made of aluminum on the semiconductor wafer surface. In such case, in order to make up for contact deficiency due to variations in the electrode height between the electrode pad of the semiconductor wafer and the head electrode of the measurement equipment, a contact sheet having conductiveness only in the film thickness direction is put usually between theses electrodes so that the examination can be accomplished. This contact sheet is called an anisotropic conductive film (or “an anisotropic conductive sheet”) because of the characteristic that the conductiveness is exhibited only in the film thickness direction at a conductive part (which is also called “an electrically conductive path” or “electrode part”) arranged according to the pattern that corresponds to a surface electrode.
In the field of electronics technology in the past, an anisotropic electrically conductive part 61 as shown in FIG. 6 has been known for the purpose of connecting a packaged integrated circuit with a printed circuit board. In the anisotropic electrically conductive part 61, conductive parts 62 are formed such that a flat porous flexible material 63 is used as an insulation part of non-conductiveness, and such that a conductive metal is filled in a section demarcated at least in one vertical direction (Z-axis direction) and is fixed with an adhesive of epoxy resin or the like. An example of such anisotropic electrically conductive parts is described in Japanese translation of PCT international application No. 10-503320. However, this anisotropic electrically conductive part 61 is not suitable for an anisotropic conductive film used in a burn-in test in which repeated use is needed. When the anisotropic electrically conductive part 61 is used as an anisotropic conductive film for the burn-in test, the conductive parts 62 are buckled by pressing applied during inspection and are unable to exhibit elastic recovery. Therefore, they must be discarded once they are used in an inspection. This results in costly inspection.
Also, Japanese Patent Application Publication No. 10-12673 discloses a sheet 71 for mounting semiconductor device. The sheet 71 is structured such that, as shown in FIG. 7, electrically conductive paths 72 are formed by providing a plurality of through-holes in an insulation sheet for sealing 74 in the film thickness direction thereof, which sheet is made of thermoset resin such as an epoxy resin material, and by filling the through-holes with an electrically conductive path material which is formed in a manner such that electrically conductive particles 73 are dispersed in an elastomer. The electrically conductive particles that are used in such case are, for example, metal or alloy particles, or capsule-type electrically conductive particles having a structure in which a conductive metal is plated on the surfaces of polymer particles.
When the sheet 71 for mounting a semiconductor device is pressed in the film thickness direction, the elastomer of electrically conductive paths 72 is compressed such that the electrically conductive particles 73 are connected together so that electrical continuity is obtained only in the film thickness direction of the electrically conductive path. However, when the sheet 71 for mounting a semiconductor device is used for a burn-in test, the anisotropic conductive film needs a high compressive load to achieve conductiveness in the film thickness direction and moreover the elasticity thereof deteriorates with the deterioration of the elastomer. Accordingly, it is not possible to use the sheet 71 repeatedly in a burn-in test. Therefore, the sheet having such structure for mounting a semiconductor device is not suitable for an anisotropic conductive film used in a burn-in test of semiconductor wafers and the like.
On the other hand, an anisotropic conductive film which is used as an interposer for the burn-in test of semiconductor wafers is required to have a function of stress relaxation in addition to a function of connecting a surface electrode of the semiconductor wafer with a head electrode of measurement equipment and connecting a wiring from the semiconductor wafer with a terminal of a semiconductor package, and so on. Therefore, the anisotropic conductive film must have elasticity in the film thickness direction so as to be able to have conductiveness in the film thickness direction at a low compression load, and in addition, must have a property of elastic recovery suitable for repeated use. Also, it is demanded that the pattern of the size and pitch of conductive parts of the anisotropic conductive film to be used in the inspection be made finer in accordance with high density packaging. However, according to conventional techniques, anisotropic conductive films that can meet these requirements sufficiently could not be developed.